Bone conduction hearing device



Aug. 16, 1938. E. H. GREIBACH BONE comnucwxon HEARING DEVICE Filed Nov. 11, 1933 2 Shee ts-Sheet l INVENTOR EMIL HENRY GREIBACH BY ATTORNEY Aug. 16, 1938.

E. H. GREIBACH BONE CONDUCTION HEARING DEVICE Filed NOV. 11, 1935 2 Sheets-Sheet 2 INVENTOR EMIL HENRY GREIBACH ATTORNEY Patented Aug. 1c, 1938 UNITED STATES PATENT orrlcs memes BONE connuc'rron nnaamo Davies Emil Henry Greib a ch, iii-mm, N. 1. Application November 11, 1933, Serial No. 687,818

(01. ire-ion 48 Claims.

in contact with hearing-inducing ;bones of the user and is powerful enough for imparting to the bones the vibratory energy required for conducting the sound vibrations over the bones of the head to the hearing nerves of the inner ear and induce hearing. I

In the bone conduction receiver of the invention a vibratory structure which is set into vibrations by electric oscillations of the audible frequency range has one of its vibratory portions coupled to hearing-inducing bones of the user so as to support in a floating condition another vibratory portion having sumcient inertia and being subjected to sufllcient acceleration for imparting through its inertia reaction vibratory energy to the hearing inducing bones.

:In such bone conduction receiver the coupled vibratory portion may be utilized to form a protective casing around the floating vibratory portion so as to prevent the pressure with which the coupled vibratory portion is held against the bones from affecting the efilciency of the vibratory motion between the floating and coupled vibratory portions of the vibratory structure. Such boneconduction receiver may be made in the form of a tiny vibratory casing carrying in its interior the floating vibratory driving mass portion which is instrumental in producing the inertia reaction hearing-inducing forces transmitted through the casing to the bone structure.

The foregoing and other objects of the invention will be best understood from the following description of the exempliflcations thereof illustrated in the accompanying drawings in which Fig. 1 is a diagrammatic view of a wearable bone conduction hearing aid showing a bone conduction receiver of the invention worn on the head of a deafened person;

Fig. 2 is an enlarged sectional view of a bone conduction receiver exemplifying the invention;

Figs. 2 and 4 are'vertical and horizontal sectional views, respectively, along lines 33 and fl-4 of Fi 2; I

Fig. 5 is an enlarged sectional view of another bone conduction receiver exemplifying the invention;

Figs. 6 and 7 are vertical sectional views, re-

. spectively, along lines 6-6 and 1'I of Fig. 5;

REISSUEB tional views, respectively, along lines 9-9 and Iii-i0 of Fig. 8;

Figs. 11 and 12 are sectional views of other types of bone conduction receivers exemplifying the invention. U

It has long been known that the majority of the deafened persons have impaired middle ears and can hear much better sound vibrations conducted through the bones of the head to the inner car than sound transmitted through the air in the ear canal. However, prior to the present invention, only telephone hearing aids which transmitted sound through air in the ear canal and the middle ear have been available for the deafened. All prior efforts to make a bone conduction hearing device followed the principles underlying the telephone receivers and utilized an externally supported heavy driving mass of a vibratory structure for vibrating a driven vibratory member pressed against the bones. Since the bone structure is hard and not as yielding as the air, the back pressure of the bones forced the driven vibratory member against the externally supported heavy driving mass of the vibratory structure and brought about operating difllculties. As a result all prior operative bone conduction hearing devices had to be large, heavy and cumbersome.

The invention overcomes these difliculties by utilizing the principle of preservation of the centerof gravity of a moving mass system for producing by the inertia reaction of a driving floating mass portion of a vibratory structure the heaving inducing forces of small amplitude transmitted to the hard bones of the user by a driven portion of the vibratory structure which is held pressed against the hearing-inducing bones and carries in a floating condition the driving vibratory mass portion of the vibratory structure.

In accordance with the invention, a vibratory has a portion which is held coupled under pressure to hearing inducing bones of the user so as to support ina floatingposition a massive portion of the vibratory structure which has a sufficient inertia and is subjected to sumcient acceleration for producing by the inertia reaction of the floating driving mass the vibratory forces required for impressing on the vibratory portion held against the bones corresponding audiofrequency vibrations which are transmitted through the bones to the inner ear and induce hearing by bone conduction.

This arrangement makes it possible to shape the coupled vibratory portion so that it forms a casing enclosing the floating vibratory portion. As a result, the bone conduction receiver of the invention may be made in the form of a very small vibrating casing which, is held pressed forces to the bones without afiecting the efficiency of the vibratory motion between the driven vibratory casing which is held against the bones and the interior fioatingly carried driving mass portion which imparts to the casing the inertia reaction hearing inducing vibratory forces.

A wearable bone conduction hearing aid equipped with a bone conduction receiver exemplifying the principles of the invention is shown in Figs. 1 to 4. It comprises a bone conduction receiver shaped in the form of a small vibrating casing which is held pressed against hearing inducing bones of the user outside the ear canal, for instance, the mastoid bone 22, by a resilient head band 2 l of steel, for instance. The casing it consists of a rigid base 23 and a rigid cover 2d suitably secured to the base and engaged by the head band 2! so as to press the casing 20 against the bones 22.

The receiver casing 20 is a part of a vibratory structure formed of an electromagnetic vibrating unit comprising a magnetic armature core 3! clamped to the base 23 and carrying on a resilient magnetic armature diaphragm 32 a floating magnetic core 33 having a central pole piece 3d forming with the adjacent 'face of the armature a small magnetic gap. The vibratory structure is actuated with electric audiofrequency current oscillations supplied through terminal bushings 35 provided in a terminal block extending from the base 23 to the actuating windings of coil 36 mounted on'the pole piece as so as to produce a vibratory motion between the mass of the floating core 33 and the armature core 3i which forms a part of the casing 28.

The floating core 33 has a substantial mass and its inertia resists the vibratory motion. As a result the floating core 33 acts as a driving member and exerts on the armature core at and the casing 20 which is coupled to the hard bones of the head inertia reaction forces proportional to the floating mass and the acceleration imparted to it by the electric current oscillation in the windings of the coil .36. Since the casing 20 and armature 3i which is clamped to it are in engagement with the bones, these inertia reaction forces drive the casing against the hard bones and impress on the bones relatively large oscillatory inertia reaction forces of small amplitude which are conveyed through the bones to the hearing nerves where they induce hearing corresponding to the audiofrequency oscillations impressed on the vibratory structure.

Although the principles underlying the hon conduction receiver using an electromagnetic vibrating structure shown in Figs. 2 to 4, lends.

of highly efficient vibrating structures with very small magnetic operating gaps of less than one thousandth of an inch. Such design assures extremely efilcient operation of electro-magnetic bone conduction receivers, and makes possible the construction of bone conduction receivers of ex tremely small size and relatively large Lower output required for satisfactory wearable bone conduction hearing aids.

Inertia reaction bone conduction receivers of the invention constructed with electromagnetic vibrating structures have also the further ad- In Fig. .1 is shown how the electro-magnetic inertia reaction bone conduction receiver of the invention is connected in the operating circuit of a prior-art wearable hearing aid. A conventionally illustrated microphone transmitter 40 is connected in series with a supply battery M and a cut-off switch $2 to the actuating coil 83 of a conventionally illustrated amplifier microphone 4% which is connected in series with the battery M and the cut-off switchdZ by way of a rheostat 5 to the leads 46 which have terminal plugs engaging the terminal bushings 35 on receiver casing and lead to the actuating winding 36 of the receiver.

With such wearable hearing aid assembly, sound waves of the principal audible frequency range, or the frequency range of intelligible speech, impinging on the microphone transmitter Ml will produce in the primary circuit including the amplifier winding 43 corresponding electric audiofrequency oscillations and actuate the amplifier microphone 46 to produce corresponding amplified oscillations which are delivered to the energizing coil 36 of the bone conduction receiver which is held pressed against the bones and transmits through the bones corresponding inertia reaction hearing inducing vibratory forces to the which the core piece 34 is joined of opposite polarity.

The end surfaces of the two outer core arms of the floating core 33 have their outer surfaces on the same level as the pole face of the central core 3%, their surfaces being preferably ground to the same level. The armature diaphragm 32 is made of a magnetically conducting spring steel and has its center portion stiffened by integrally uniting it, as by soldering or brazing, to a heavy rigid anchoring cross bar 5| of iron, for instance, extending transversely across the diaphragm 32.

The central'portion of the armature diaphragm 32 extends over the full length of the cross bar SI and is integrally united thereto as by soldering or brazing. The center portion of the anchor bar M is provided with a threaded hole 2l8 in which is threadedly mounted the armature core 3| having at its exterior end a slot for turning it to adjust the distance of its pole face from the pole'face of the core piece 34;

The end portions of the cross bar 5! are undercut and fit the side walls of a groove provided in the base 23 of the receiver, which may be molded of a synthetic resin. The cross bar Si is tightly clamped to the base 23 by four screws 53 which are screwed into metal anchors 56, imbedded within the base. An opening in the base 23 is enclosed by sealing plug 55 to give access to the groove of the armature 3| for adjusting the gap.

Once the adjustment is made, the armature 3| may be locked in place, for instance, by a lock with a lock spring 53 arranged similar to a familiar snap fastener is embedded in the wall of the cover 24, and a shank 80 extending from the head band has a ball-shaped end which may be inserted into the socket to form with it a detachable universal joint connection. This universal joint connection assures that, when the head band 2| presses the receiver casing 20 against the bones, the'contact surfaces of the receiver will automatically adjust itself to secure an eflicient coupling engagement with the bones.

Insteadof a head band, any other suitable arrangement for coupling the receiver structure to the bones may be used.

In manufacturing the bone conduction receiver of Figs. 2 to 4, the floating core 33 with the coil 36 and the armature'diaphragm 3|32 with the cross bar 3| may be assembled as a self-contained unit and the gap between the armature 3| and the core piece 34 adjusted by turning the armature 3| until its pole face contacts with the core piece 34. 'I'hereupon the armature 3| is turned back on its thread until a magnetic gap of the desired small length is provided between the adjacent pole surfaces and the armature 3| -is locked in place. In this adjusted position the assembled vibrator structure may be tested and after final adjustment clamped to the base 23.

A practical bone conduction receiver con structed as shown in Figs. 3 to 4, with the following principal dimensions, will give satisfactory results: Permanent magnet core of a total outer length of 1"; a core thickness of a core height of about V4"; a core width of about 1 acenter core diameter of about .120"; and a diaphragm thickness of about .014".

Because; of the relatively large mass of the head, the coupled portion of the receiver will under the action of the vibratory forces have only an imperceptible vibratory movement and will be practically stationary. As a result of this vibratory movement, relatively large reactive forces will be'imparied by the mass of the floating core to the bones of the head, transmitting thereto vibrations of small amplitude and large force sufllcient to convey by bone-conduction speech and music to the auditory center of the head. The magnetic gap is made very small, of the order of a mil or less, thereby ,securing a high negative stiffness and efllcient vibrations. The armature diaphragm 32 is made of sufllcient cross section to permit flow of a strong permanent flux through the gap and also to permit inducing strong alternating fluxesthrough the magnet gap by the action of the sound-frequency current oscillations passingthrough the actuating coil. The thickness of the armature dia-. phragm is made large enough to overcome the" vnegative stiffness-and secure stable vibrations underthe action of the fluctuating magnetic fleld in the gap.

By making the joint between the diaphragm 32 and the bar 5| by which it is heldclamped to the base solid and firm, as by soldering, the

center portion of the diaphragm strip does not participate in the vibratory movement of the lateral diaphragm portions, eliminating distortion 7 that might occur otherwise. By providing at the ends of the diaphragm 32 reinforcing strips 51 whichare integrally united with the diaphragm, disturbances due to non-uniform clamping of the diaphragm ends are prevented. eliminating distortion.

The high negative stiffness secured by the small magnetic gap enables the use of a relatively thick diaphragm 32 having sufficient cross section for carrying the flux while at the same time making its effective stiffness opposing the negative magnetic stiffness sufflciently small to operate with a resonance frequency at which good response is secured over a large sound-frequency range.

In the electromagnetic bone conduction receiver described in connection with Figs. 2 to 4, the relatively large floatingly mounted vibratory mass of thereceiver is utilized to produce the inertia reaction forces required for imparting hearing by bone conduction and a very stiff spring member is utilized to carry the floating vibratory mass so as to give a" resonance frequency which assures a good response over the speech frequency range. Theuse of such stiff spring makes possible the operation of the electromagnetic vibrating structure with an extremely small magnetic gap distance at which the high flux densities and large magnetic forces in the gap do not produce fringing or freezing of the pole faces bordering the gap. Such small gaps are made possible by the utilization of the coupled vibratory portion of the vibrating structure as casing which protects the floating mass against any disturbance by external forces. This combination of elements assures an extremely emcient vibratory structure and makes possible the development of relatively large power in a very small receiver unit.

In Figs. 5 to 7 is shown a bone conduction receiver of the invention constructed with a cantilevertype vibratory structure for producing the inertia reaction forces required for inducing hearing by bone conduction. It comprises a vibratory casing, formed of'a rigid base 10 and a cover ll, held pressed against hearing inducing bones 22 by ahead band 2| engaging a channel member formed in the cover H. The casing 'I3 is a part of a vibratory structure of the cantilever-type formed of a U-shaped permanent magnet core 12 floatingly supported by a spring 13 clamped to a block I4 extending fromthe base 10, and pole pieces 15 extending from the arms of the magnet core 12 to form magnetic gaps with a magnetic armature core 13 clampedto the base of the casing. A vibratory motion is produced between the floating magnet core I2 and the armture 16 with its casing Ill-ll i5 and the armature I3 is very small, relatively large inertia reaction forces will be exerted by the floating core 12 on the armature I6 and ducing hearing by bone conduction.

In order to secure efficient operation of the vibratory structure with a very tiny gap of the order of one thousandth of an inch or less, the spring 13 has a longitudinal slot for permitting adjustment of the position of the floating magnet core 72 on the spring 13 so as to assure operation at a minimum gap distance between the pole faces of the pole pieces i5 and the armature it without causing fringing of the adjacent pole f ces.

In Figs. 8-10 is shown a bone conduction re-' oeiver embodying a balanced magnetic vibratory structure for producing the inertia reaction hearing-inducing vibrations.

It comprises a vibratory casing formed of a base 88 and a cover 8! held pressed against hearing inducing bones 22 by a head band 2! having a universal joint connection with the cover 8|, as in the bone receiver of Figs. 2 to 4. The casing 808i is a part of a vibratory structure formed of a magnetic armature core 82 having its opposite ends clamped to two base projections -83 and carrying on 'its magnetic diaphragm extensions 86 a floating balanced magnetic core system formed of magnetic core blocks 81 and core bars 85 having centralcore pole pieces 86 facing the opposite faces of the armature 82 to form therewith two magnetic gaps. The magnetic systemis magnetized so that the two pole pieces 85 are of opposite polarity and pass a permanent magnetic flux from one pole piece 86 across the armature 82 and its two gaps to the other pole piece 86, the path of the permanent flux being completed by the magnetic core blocks Bl through which the' ends of the opposite magnet bars 85 are clamped to the reinforced ends of the diaphragm 84 without using the diaphragm extensions as for carrying the permanent flux.

'On each pole piece 86 are mounted coils of actuating windings 88 which are supplied with electric audiofrequency oscillations through terminal bushings 89 mounted on a terminal block extending from the base 80. The two coils 88 are so connected that when actuated by audiofrequency current oscillations the flux in .one magnetic gap is reduced while it is increased in the other gap, the diaphragm extensions 86 serving as return paths for'the alternating flux. Since the armature 82 is rigidly clamped to the base 8d, the audiofrequency flux variations in the two armature gapswill produce a vibratory motion between the floating core bars 85 and the armature 82 and the inertia reaction of the floating mass will exert on the armature 82, and therethrough, by way of the casing wall, on the bones of the user, inertia reaction forces which induce hearing by bone conduction.

To secure emcient operation of the magnetic vibrating structure, the core pole pieces 86 are threadedly mounted in holes ,of the magnet bars 55 so as to make possible adiustment of the gaps betwen the pole faces of the core pieces 86 and the gap faces of the armature 82 at which the gaps will be a minimum without causing fringing of the adjacent pole faces during the bone conduction receiver of the invention, of.

the type shown in Figs. 8 to 10, even harmonic 'therethrough over the casing to the bones for indistortion is eliminated and objectionable saturation of the flux paths is avoided.

Since the permanent flux acting on the opposite pole faces of the armature is balanced, the.

armature diaphragm is not subjected to any permanent deflection. Furthermore, the maximum amplitude of the vibrations between the armatureand the floating core is limited by the small magnetic gaps of the order of one thousandth of an inch on the opposite sides of the armature.

Accordingly, flexing of the armature diaphragm beyond its elastic limit is prevented, and even if the receiver is dropped, and the momentum of the heavy floating mass tends to impart a large deflection to the armature diaphragm, this deflection will be limited by the small gaps on the opposite sides of the armature to a value at whichthe elasticity of the diap .will automatically restore the normal gap spacign.

As a result, the receiver may be dropped without damage, and it may be operated with smaller gaps than receivers without balanced magnetic core systems, thereby increasing its efiiciency.

In Figs. 10 and 11 are shown two other exempliflcations of an inertia reaction bone conduction receiver of the invention. In the arrangement of Fig. 10, a receiver housing formed of a casing Bil and a top wall 99 has clamped to the top wall 9i an extension of a magnetic core piece 92 on which is mounted a magnetic diaphragm 93 carrying a floating U-shaped magnet core 94 which has a central pole face forming a magnetic gap with the pole face of the core piece as. The vibratory structure is actuated by a coil 85 mounted on the core piece 92 clamped to the top 9! of the casing to produce under the action of audiofrequency currents a vibratory motion between the floating core 94 and the core piece 92. As a result, the inertia reaction of the floating core exerts hearing inducing vibratory forces on the core piece 92 and therethrough, over the casing 9! on the hearing-inducing bones engaged by the casing.

The casing of the bone conduction receiver shown in Fig. 10, is illustrated in the form of a bridge member of a spectacle frame and its exterior walls are shown curved to form a concave contact surface for securing intimate coupling engagement with the bones 22 of the nose and secure an eflicient transmission of the hearing-inducing vibratory energy from the receiver casing to the bones.

In the arrangement of Fig. 11 is shown an inertia reaction bone conduction receiver of the invention having an electromagnetic vibrating structure similar to that shown in Figs. 2 to 4. It comprises a floating magnetic core 33 carried by an armature diaphragm 32 which is clamped to a wall of an enclosing casing 86 having a projecting contact member 91 with a curved concave contact surface held in engagement with hearing inducing bones 22 of the user. This bone conduction receiver is likewise designed for mounting in a. bridge member of a spectacle frame 98 forming a housing around the receiver casing 96 and supporting it between two springs 99 so as to prevent the inertia reaction vibrations of the receiver casing 96 which are-transmitted by the contact member 91 to the bones of the nose from being transmitted to the spectacle frame $8.

The performance and the quality of the reproduction in the bone conduction receivers of the invention described above may be increased without increasing their weight and size by employing instead of ordinary steel diaphragms special materials of high magnetic permeability, such as Hypernik, A-metal, or Permaloy. These materials have a much higher magnetic permeability than ordinarily used spring steel. They accordingly reduce the flux reluctance and enable development of larger fluxes increasing the power output of a given size and weight of structure In the bone conduction receivers described above, such high permeability materials may be used notwithstanding their relatively smaller elasticity, because the small amplitudes with which the diaphragms are required to operate produce only small strains in such diaphragms, and these strains are within their elasticity limits. By using such materials for diaphragms, they may be given a relatively great thickness without unduly increasing their stiifness, thus providing a large cross section of highly permeable magnetic material for producing a large flux and providing at the same time the required elasticity for operating with e desirable degree of stillness.

The principles of the invention described above in connection with various types of electromagnetic vibrating structures will suggest to those skilled in the art many other ways of making small inertia reaction bone conduction receivers with various other types'of vibratory structures. It is accordingly desired that the appended claims be given a broad. construction commensurate with the scope of the invention within the I claim:

1: In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, a vibratory structure comprising a driven magnetic core portion having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user, and a driving fioatingly carried magnetic core portion resiliently joined to said driven core portion to form therewith a magnetic flux path ineluding a gap, and means for actuating said vibratory structure with electric oscillations substantially throughout the speech frequency range to produce corresponding vibrations of said core members'across said gap, said driving core por-- tion having a sufliciently large mass andexerting under the action of the electric oscillations sufiicient inertia reaction forces upon said driven core portion and therethrough upon the coupled I bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

2. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure comprising an "elastically deformable magnetic core member forming a magnetic flux path including a gap, said core member having a driven core portion with a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user and a'driving core portion floatingly carried relatively to said driven core portion, and windings interlinked with said flux path for actuating said vibratory structure with electric oscillations of.

the principal audible frequency range to produce corresponding vibrations of said core portions across said gap, said driving core portion havmg a sufliciently large mass and exerting under the,action of the electric oscillations sumcient inertia reaction forces through said contact surface upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the 'inner ear and induce intelligible hearing.

3. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure having a driving magnetic core memberand a driven magnetic core member resiliently joined into a magnetic flux path including a gap, means for holding said driven core member: coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying said driving core member in a floating condition, and windings interlinked with said flux path for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a suflicientiy large mass and exerting under the action of the electric oscillations sufllcient inertia reaction forces upon said driven co're member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

4. In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person a vibratory member comprising two resiliently joined magnetic core portions forming a magnetic flux path including a gap, one of said core portions having a rigid contact surface element arranged to be held coupled under pressure to hearing inducing bones of the user and floatingly carrying another of said coreportions, and means for actuating said vibratory member with electric oscillations substantially throughout the speech frequency range to produce corresponding vibrations of said core portions across said a gap, said fioatingly carried core portion having Junction between said core portions being suf-' ficiently large to secure a vibratory motion of said core portions at a gap spacing of less than four thousandths of an inch without fringing of said gap.

. 5. In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person a vibratory member comprising two resiliently joined magnetic core portions forming a magnetic flux path including a gap, one of said core portions having a rigid contact surface element arranged to be held coupled under pressure to hearing inducing bones of the user and floatingly carrying another of said core portions, and means for actuating said vibratory member with electric oscillations substantially throughout the speech frequency range to produce corresponding vibrations of said core portions across said'gap, said floatingly carried core portion having a suificiently large mass and exerting under the action of the electric oscillations sufllcient inertia reaction forces upon said contact surface element and therethrough upon tlie coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiflness of the ghearlngeinducing bones of the user, said driving ing of said gap, said contact surface element being arranged and shaped to protect said floatingly carried core portion against external forces.,

6. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure having a driving magnetic core member and a driven magnetic core member resiliently joined into a magnetic flux path including a gap, said driven core member having a contact surface arranged to be held coupled under pressure to core member being fioatingly carried relatively to said driven core member, and windin s interlinked with said flux path for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce for inconspicuous wear by a user, a vibratory structure having a driving magnetic core member and a driven magnetic core member resiliently joined into a magnetic flux path including a gap, means for holding said driven core member coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying said driving core member in a floating condition,

and windings interlinked with said flux path for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a sufliciently large mass and exerting under the action of the electric oscillations suficient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, said driven core member being arranged and shapedto protect said driving core member against external forces.

8. In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, a vibratory member having two resiliently- Joined magnetic core portions forming a magnetic flux path including a gap, one of said core portions forming part. of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user and floatingly carrying another of said core portions 7 core portion having a sufiiciently largemass and exerting under the action of the electric oscillations sufficient inertia reaction forces upon said casing and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

9. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user and a driving 'floatingly carried magnetic core member resiliently joined to said driven core member within said casing to-form therewith a I magnetic flux path including a gap, and windings interlinked with said flux path for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a sufiiciently large mass and exerting under the action of the electric oscillations sumcient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for impart ing thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said core members being sufllciently large to secure a vibratory motion of said core members at a gap spacing of less than four thousandths of an inch without fringing of said gap.

10. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure having a driving magnetic core member and a driven magnetic core member resiliently joined into a magnetic flux path including a gap, said driven core member forming a part of a rigid casing having a contact surface arranged for coupling under pressure to hearing inducing bones of the user, said driving core member being floatingly carried relatively to said driven core member within said casing, and windings interlinked with said flux path for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a mass .sufllciently larger than the mass of said driven core member and exerting under the action of the electric oscillations sufficient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for'lmparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

11. In an inconspicuous bone conduction hearing device, a vibratory structure comprising a rigid vibratory casing having an external contact surface arranged for coupling under pressure to hearing inducing bones of the user and a driven magnetic core portion operatively exposed to the interior of said casing, a driving magnetic core portion resiliently carried in a floating condition within said casing to form with said driven core portion a magnetic flux path including a gap, and

' means for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said resiliently carried driving core portion having a sufiiciently large mass and exerting under the action of the electric oscillations sufliclent inertia reaction forces upon said casing and therethrough upon said bones for imparting thereto vibratory energy required'for transmitting corresponding vibrations through the bones to the innerear of the user and induce intelligible hearing.

12. In an inconspicuous hearing imparting device. a vibratory structure comprising a rigid vibratory casing having an extended external vibration transmitting surface and a driven magnetic core portion operatively exposed to the interior of said casing, a driving magnetic core portion resiliently carried in a floating condition within said casing to form with said driven core portion a magnetic flux path including a gap, and means for actuating said vibratory structure with electric' oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said floatlngly carried magnetic core portion having a mass sumciently larger than the mass of said casing and exerting under the action of the electric oscillations sufllcient inertia reaction forces upon said casing for imparting thereto vibratory energy required for transmitting from the external surface of said casing corresponding vibrations' to the inner ear of the-user and induce intelligible hearing.

13. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure having a driving magnetic core member and a driven magnetic core member resiliently joined into a magnetic flux path including a gap, means including a casing for holding said driven core member coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying saiddriving core member in a floating condition within said casing, and windings interlinked with said flux path for actuating said vibratory structure with electric oscillations of the Principal audible frequency range to produce corresponding vibrations of said core members acrosssaid gap, said driving core member having a sumciently large mass and exerting under the action of the electric oscillations sumcient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

14. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user, and a driving floatingly carried magnetic core member resiliently joined to said driven core member within said casing to form therewith a magnetic flux path including a gap. and windings interlinked with said flux path for actuating said.

vibratory structure with electric oscillations of the principal audible frequency range to produce I corresponding vibrations of said core members across said gap, said driving core member having 7 a suiliciently large mass and exerting under the sandths of an inch without fringing of said. gap.

15., In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, a vibratory structure having a driving magnetic core member and a driven magnetic core member resiliently joined into a magnetic flux path including a gap, said' driven core member forming a rigid casing having a contact surface arranged to be held coupled under pressure to hearing inducing bonesof the user outside the ear canal, said driving core member being floatingly carried relatively to said driven core member within said casing and windings interlinked with said iiux path for actuating said vibratory structure withelectric oscillations substantially throughout the speech frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a sufflciently large mass and exerting under the action of the electric oscillations sumcient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said core members being sumciently large tosecure a vibratory motion of said core members at a gap spacing of less than four thousandths of an inch without fringing of said gap.

16. In a bone conduction hearing device suitable for inconspicuous wearby a user, a vibratory structure comprising a driven magnetic core member forming part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user and a driving fioatingly carried magnetic core member resiliently joined to said driven core member within said casing to form therewith a magnetic flux path including a gap, and means for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a mass sumciently larger than the mass of said driven core member and exerting uriderthe action of the electric oscillations sufilcient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stifiness of the resilient junction between said core members being sufflciently large to secure a vibratory motion of said core members at a'gap spacing of the order of one thousandth of an inch without fringing of said gap. '11. In a bone conduction hearing aid devi suitable for inconspicuous wear by a deafened person, avibratory structure having a driving magnetic core member and a driven magnetic core member resiliently joined into a magnetic .flux path including a gap, said driven core member forming a rigid casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user outside the ear canal, said driving core member being floatingly carried relatively to said driven core member within said casing, and windings interlinked with said flux path for actuating said vibratory structure with electric oscillations substantially throughout the speech frequency range to produce corresponding vibrations of said core members across said gap said driving core member of said driven core member and exerting under the action of the electric oscillations suflicient inertia. reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said core members being sufliciently large to secure a vibratory motion of said core members at a gap spacing of the order of one thousandth of an inch without fringing of said gap.

18. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user and a driving floatingly carried magnetic core member resiliently joined to said driven core member within said casing to form therewith a magnetic flux path including a gap, and windings interlinked with said driving core member for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a sufficiently large mass and exerting under the action of the electric oscillations suflicient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said core members being sufliciently large to secure a vibratory motion of said core members at a gap spacing of less than four thousandths of an inch without fringing of said gap.

19. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a rigid casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user, and a driving fioatingly carried magnetic core member resiliently joined to said driven core member within said casing-to form therewith a magnetic flux path including a gap, and windings interlinked with said driven core member for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a suinciently large mass and exerting underthe action of the electric oscillations suflicient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to theinner ear and induce intelligible hearing, the stiffness of the resilient junction between said core members being sufficiently large to secure a vibratory motion of said core members at a gap spacing of less than four thousandths of an inch without fringing of said gap.

. '20. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user and a driving floatingly carried magnetic core member resiliently joined to said driven core member within said casing to form therewith a magnetic flux path including a gap, and windings interlinked with said driving core member for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a mass suiiiciently larger than the mass of said driven core member and exerting under the action of the electric oscillations suificient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said core members being sufflciently large to secure a vibratory motion of said core members at a gap spacing of the order of one thousandth of an inch without fringing of said gap.

21. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user and a driving fioatingly carried magnetic core member resiliently joined to said driven core member within said casing to form therewith a magnetic flux path including a gap, and windings interlinked with said driven core member for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a suficiently large mass and exerting under the action of the electric oscillations sufiicient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said core members being sumciently large to secure a vibratory motion of said core members at a gap spacing of less than four thousandths of an inch without fringing of said gap.

22. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a rigid casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user, and a driving floatingly carried magnetic core member resiliently joined to said driven core member within said casing to form therewith a magnetic flux path including a gap, and windings interlinked with said driven core member for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a sufficiently large mass and exerting under the action of the electric oscillations suiilcient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stifi'ness oi the resilient Junction between said core members being sumciently large to secure a vibratory motion of said core members at a gap spacing of less than four thousandths of an inch without fringing of said gap.

23. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user and a driving floatingly carried magnetic core member resiliently joined to said driven core member within said casing to form therewith a magnetic flux path including a gap, and windings interlinked with said driven core member for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a mass sufficiently larger than the mass of said driven core member and exerting under the action of the electric oscillations sufiicient inertia reaction forces, upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said core members being sufli ciently large to secure a vibratory motion of said core members at a gap spacing of less than four thousandths of an inch without fringing of said gap.

24. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure having two resiliently joined core portions forming a magnetic flux path including two gaps, one of said core portions having two surfaces on opposite sides of said one core portion forming pole faces for said two gaps, the other core portion having two pole surfaces facing said pole faces on opposite sides of said two gaps, and windings interlinked with said flux path for actuating said core portions with electric oscillations substantially throughout the speech frequency range for producing corresponding vibrations of said core portions across said two gaps so as to increase one gap while the other gap is decreased, a casing for holding one of said core portions coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying the other of said core portions in a floating condition with said casing, said floating core portion having a sumciently large mass and exerting under the action of the electric oscillations sufficient inertia reaction forces upon said coupled core portion and therethrouh upon the coupled bones for imparting thereto the vibratory energy required for conducting. corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

25. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory,

structure having a driving magnetic core member and a driven magnetic core member resiliently joined to form a magnetic flux path including two gaps, said driven core member having a set of two surfaces on opposite sides of said driven core member formingpole faces for said two gaps, said driving-core member including core portions extending toward the pole faces of said driven core member to form the opposite pole faces of said two gaps, and windings interlinked with said flux path for actuating said core members with electric oscillations of the principal audible frequency range for producing corresponding vibrations of said core members across said two gaps so as to increase one gap while the other gap is decreased, means including a rigid casing for holding said driven core member coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying said driving core member in a'floating condition within said casing, said driving core member having a suffrciently large mass and exerting under the action of the electric oscillations suificient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

26; In a bone conduction'hearing device suitable for inconspicuous wear by a user, a vibratory structure having a driving magnetic core member and a driven magnetic core member resiliently joined to form a magnetic flux path including two gaps, said driven core member having a set of two surfaces on opposite sides of said driven core member forming pole faces for said two gaps, said driving core member including core portions extending toward the pole faces of said driven core member to form theopposite pole faces of said two gaps, and windings interlinked with said flux path for actuating said core members with electric oscillations of the principal audible frequency range for producing corresponding vibrations of said core members across said two gaps so as to increase one gap while the other gap is decreased, means including a casing for holding said driven core member coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying said driving core member in a floating condition within said casing, said driving core member having a mass sufliciently larger than the mass, of said driven core member and exerting under the action of the electric oscillations suflicient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said core members being sufiiciently large to secure a vibratory motion of said core members at a gap spacing of less than four thousandths of an inch without fringing of said gap.

2'1. The method of inducing hearing with an electromagnetic vibratory hearing aid structure having two resiliently joined magnetic core members that vibrate under the action of electric oscillations of the audible frequency range, which resides in holding one core member coupled under pressure against hearing inducing bones of the user so as to carry the other core member having a relatively large mass in a floating condition, and utilizing the fioatingly carried core member to exert vibratory inertia reaction forces upon the coupled core member and therethrough upon the bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

28. The method of inducing hearing with a vibratory hearing aid structure that vibrates under the action of electric oscillations of the audible frequency range, which resides in holding a vibratory portion of said structure coupled under pressure against hearing inducing bones of the user so as to carry the other vibratory portion of said structure having a relatively large mass in a floating condition, and utilizing the floatingly carried' vibratory portion to exert vibratory inertia reaction forces upon the coupled vibratory portion and therethrough upon the. bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

29. In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, an elastically deformable vibratory member having two vibratory portions and means for actuating said vibratory member with electric oscillations substantially throughout the speech frequency range for producing corresponding vibrations of said vibratory portions, one of said vibratory portions having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user and fioatingly carrying the other of said vibratory portions, the iioating vibratory portion having sufllcient mas and exerting under the action of the electric oscillations suflicient inertia reaction forces upon I the coupled vibratory portion and therethrough upon the coupled bones of the user for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing.

30. In a bone conduction hearing device suitable for inconspicuous wear by the user, an elastically deformable vibratory member comprising a drivenvibratory portion having a contact surface element arranged to be held coupled under pressure to hearing inducing bones of the user and a driving vibratory portion floatingly carried relatively to said contact surface portion, and means for actuating said vibratory member with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said vibratory portions, said fioatingly carried vibratory portion having sufficient mass and exerting under the action of the electric oscillations sufiicient inertia reaction forces upon the contact surface element and therethrough upon the bones of the user for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce therein intelligible hearing.

31. in a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, an elastically deformable vibratory memher having two vibratory portions and means for actuating said vibratory member with electric oscillations substantially throughout the speech frequency range for producing corresponding vibrations of said vibratory portions, one of said vibratory portions having a rigid contact surface element arranged to be held coupled under pressure to hearing inducing bones of the user and floatingly carrying the other of said vibratory brations through the 'bones to the inner ear of the user and induce intelligible hearing.

32. In a bone conduction hearing device suitunder pressure to hearing inducing bones of theuser outside the ear canal and carrying the other vibratory portion of said vibratory structure in a floating condition, said floating vibratory portion having suilicient mass and exerting under the action of the electric oscillations suflicient inertia'reaction for imparting to the coupled bones of the user the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing.

33. In a bone conduction hearing device suitable for inconspicuous wear by the user, a vibratory structure having one vibratory portion with a contact surface arranged for coupling under pressure to hearing inducing bones of the user and another vibratory portion floatingly carried by said bone coupled vibratory portion, means for actuating said vibratory structure with electric oscillations of the principal audible frequency range for producing corresponding vibrations between said vibratory portions, the floatingly carried vibratory portion having a mass sumciently larger than the mass of said bone coupled vibratory portion and exerting under the action of the electric oscillations sufficient inertia reaction forces upon the bone coupled vibratory portion and therethrough upon the bones of the user for imparting thereto the vibratory energy required for conducting corresponding vibrations through the coupled bones to the inner ear of the user and induce intelligible hearing.

34. In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, a vibratory structure having two vibratory portions and means for actuating said vibratory structure with electricoscillations substantialiy throughout the' speech frequency range for producing corresponding vibrations of said vibratory portions, one of said vibratory portions having a rigid contact surface element arranged to be held coupled under pressure to hearing inducing bones of the user and floatingly carrying the other of said vibratory portions, said floating vibratory portion having suiiicient mass and exerting under the action of the electric oscilla tions sufiicient inertia reaction forces upon said contact surface element and therethrough upon the coupled bones of the user for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hear-- ing, said bone coupled vibratory portion being arranged and shaped to protect said floating vibratory portion against external forces.

35. In a bone conduction hearing device suitable for inconspicious wear by the user, a vibratory structure having two vibratory portions, means for actuating said vibratory structure with electric oscillations of the principal audible frequency range for producing corresponding vibrations between said vibratory portions, and means for holding one of said vibratory portions coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying the other vibratory portion of said vibratory structure in a floating condition,'the floating vibratory portion having sufiicient mass and exerting under he action of the electric oscillations sufllcient aertia reaction forces upon the bone coupled viiratory portion and therethrough upon the couiled bones of the user for imparting thereto the ibratory energy required for conducting correponding vibrations through the bones to the inierear of the user and induce intelligible hearng, said bone coupled vibratory portion being .rranged and shaped to protect said floating viratory portion against external forces.

36. In a bone conduction hearing aid device uitable for inconspicious wear by a deafened lerson, a vibratory structure having two vibraory portions and means for actuating said vibraory structure with electric oscillations substanially throughout the speech frequency range for iroducing corresponding vibrations of said vibraory portions, one of said vibratory portions orming a casing having a contact surface aranged to be held coupled under pressure to hearng inducting bones of the user, the other of said vibratory portions having suflicient mass and beng fioatingly carried within said casing so as to :xert-underthe action of the electric oscillations iuflicicnt inertia reaction forces upon the coupled vibratory portion and therethrough upon the :oupled bones of the user for imparting thereto ,he vibratory energy required for conducting corresponding vibrations through the bones to the rnrier ear of the user and induce intelligible nearing.

' 37. In an inconspicious hearing imparting 'device, a vibratory structure comprising a vibrazory casingha-ving an eirtended external vibration transmitting surface, a vibratory portion iloatlngly carried within said casing, means for actuating said vibratory structure with electric oscillations of the principal audible frequency range for producing corresponding vibrations between said floatingly carried ibratory portion and said casing, said floatingly carried vibratory portion having suflicient mass larger than the mass of said,casing and exerting under the action of the electric, oscillations suflicient inertia reaction forces upon said casing for imparting thereto vibratory energy required for transmitting corresponding vibrations from the external surface said casing to the inner ear of i the user and induce intelligible hearing.

38. In a bone conduction hearing device suit-' able for inconspicious wear by the user. a vibratory structurepomprising a driven vibratory pottion forming a part of a rigid casing. having a contact surface arranged to beheld coupled under pressure to hearing inducing bones of the user, a driving vibratory portion floatingly, carried. within said casing. and means for actuating said vibratory structure'with electric oscillations of the principal audible frequency range for producing corresponding vibrations between said vibratory portions, said driving vibratory portion having suflicient mass and ex'ertingiunder the action of the electric oscillations suflicient inertia reaction forces upon saidcasing and therethrough upon the coupledbones of the user for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing.

39,. In a bone conduction hearing device suit-.

able for inconspicious wear by the user, a vibratory structure having two vibratory portions, means i'or actuating said vibratory structure with electric oscillations of the.principal audible frequency range for producing corresponding vibrationsbetween said vibratory portions, and a rigid casing for holding one of said vibratory portions coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying the other vibratory portion of said vibratory structure in a floating condition within said casing, said floating vibratory portion having sufllcient mass and exerting under the action of the electric oscillations suflicient inertia reaction forces upon said casing and therethrough upon the coupled bones of the user for imparting thereto the vibratory energy required for conducting corresponding vlbrations through the 5 bones to the inner ear of the user and induce intelligible hearing.

-=sure to hearing inducing bones of the user, a

vibratory portion floatingly carried within said casing, and means for actuating said vibratory structure with electric oscillations of the principal audible frequency range for producing corresponding vibrations between said fioatingly carriedvibratory portion and said casing, said floaiingly carried vibratory portion having a mass sumciently larger than the mass of said casing and exerting under the action of the electric oscillations sumcient inertia reaction forces upon the casing and therethrough upon the bones of the user for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing.

41. In a portable audiphone, the combination of electromagnetic means adapted to respond to varying currents substantially throughout the 40 audible frequency range, a relatively-stiff vibrating member carrying the means and'forming a tion can'ied by said vibratory portion and including a speech coil and adapted when the coil is energized by varying currents to eflect vibration of .said vibratory portion, said electromagnetic portion having greater inertia than said vibratory, portion, andmeans' for holding the vibratory portion in operative connection with the bone structure of the user, whereby the vibrations of the vibratory portion are conducted through so the bone structure to the inner ear of the user. 43 Ina portable audiphone. the combination bfrl vibratory member, electromagnetic means earriedby the member and adapted to respond to varying currents substantially throughout the audible frequency range for vibrating said member, and means for supporting the member in operative connection with the bone structure of the usen'whereby' the vibrations of said member are conducted through the bone structure to the inner ear of the a. a. oanmscn. 

